1. Field of the Invention
The present invention relates generally to the field of matrix printing wherein alphanumeric characters are printed in dot matrix form by the energization of one or a plurality of wire elements or, print hammers, in response to digitally generated character data for driving and controlling one or more printing heads, each head including one or more of such print hammers, for sequentially printing lines of characters on a print receiving medium. The matrix printing field also includes non-impact printing such as thermal printing. More particularly, the present invention relates to a matrix printer and a novel wire matrix print head repetition rate control therefor, for varying the repetition rate of the print hammers in accordance with the speed of printing, or the rate at which the printing head or heads traverse the printing medium, thereby printing characters of constant width and clarity at varying printing speeds. The present invention also relates to the generation of variable digital clocks for clocking printing data and hammer drive pulses to a matrix print head or heads synchronously and at a rate which produces even character column spacing and constant character width regardless of variation in the speed at which characters are printed.
2. Description of the Prior Art
Modern high speed matrix printers must have print head control capable of printing a variety of character fonts at ever increasing and varying speeds, under varying input power conditions and yet maintain reliability of operation, cost efficiency, durability, uniform character spacing and width and constant print quality. While the actual print head construction does not form a part of the present invention, many configurations are possible, both with respect to the number of print wires and print wire orientations. A typical matrix print head wire matrix drive is illustrated by U.S. Pat. No. 3,690,431. A timing control of the prior art for a matrix printer is illustrated by U.S. Pat. No. 3,719,781. A dual three-station matrix printer of the prior art is illustrated by U.S. Pat. No. 3,825,681.
A digital to analog converter with amplitude and pulse-width modulation, of the prior art, is disclosed by U.S. Pat. No. 3,789,393, wherein pulse-width modulated and pulse-amplitude modulated signals are summed to derive fine data bits and coarse data bits in a position measuring apparatus.